Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. Heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability. By heating the medium, the material's magnetic crystalline anisotropy energy density or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity to assure thermal stability of the recorded information.
With the advent of such technologies, storage densities of about 1 Tbit/in2 and beyond have become highly desirable. In order to effectively create such densities, the storage media must be heated by a focused optical spot in a highly localized area. Theoretical methods of creating storage densities of up to 1 Tbit/in2 would require an optical spot having a diameter of about 25 nm. Optical spots having a diameter of about 25 nm are typically an order of magnitude smaller than optical spots that can be achieved by traditional diffraction-limited optical systems. Accordingly, traditional optical spots are too wide to achieve recording densities approaching 1 Tbit/in2.
Sub-wavelength apertures have been suggested as a way of achieving very small optical spots. However, the energy of an optical spot produced by a sub-wavelength aperture is not capable of effectively propagating through the sub-wavelength aperture, and the resulting energy throughput is very low. The resulting throughput energy must be sufficient to heat the media to sufficiently reduce coercivity. A 25 nm optical spot would need to deliver about 1 mW of power to effectively write to the media. Traditional apertures, including sub-wavelength apertures, cannot produce an optical spot having a diameter of about 25 nm capable of imparting sufficient power to the media.
Accordingly, there is a need for devices that can provide a reduced optical spot size with increased throughput efficiencies.